The Android team has a sense of humor, and has put several funny easter eggs into their code. Probably the best known easter egg is the “hidden” pseudo-game in the About Phone section. Tapping on the Android version several times launches a screen with Jelly Beans, KitKats, or other funny stuff. Now, you can port these little mini games to other Android versions.
Recognized Contributor iamareebjamal wrote a guide for Gingerbread devices, and explained what needs to be done to swap the standard easter egg screen with the one from Jelly Bean. This can be done by using reverse engineering tools like APKTool and derivatives.
The process of adding in the easter egg is pretty straightforward. You need to add a few lines of Smali code to one of decompiled files, and then recompile the framework. The changed file can then be pushed back to your device, and you can enjoy Jelly Bean easter egg or use it to fool your friends. This mod should work on almost every device running Gingerbread or Ice Cream Sandwich.